My concern would be, that if there was not enough SOM for the bacteria to work with, where would the 'nutrients cycle from'???

Well, to keep the party going, add more organic matter. In addition, much of the food for microbes is exuded by plant roots. In fact, the exudate will favor the microbes that are beneficial to the plant. Roots constantly slough of dead cells which add to SOM.

Microbes also are responsible for mining nutrients from the inorganic parent material of the soil. Mycorrhizea are critical for unlocking P and transporting it to plant roots. Certain nitrifying bacteria extract N from the air in soil pores and make it plant available.

The human part of the puzzle is to use practices which enhance rather than harm the process that builds soil health.